This invention relates to a device that is sensitive to magnetic fields having several magnetic field sensors, and more particularly to a device having several magnetic field sensors, where each sensor comprises core materials having different coercive field strengths and is formed on a substrate using a thin-film process.
In the publication "Siemens Research and Development Report", Volume 15 (1986) No. 3, pp. 135-144, a spontaneous switching effect in ferromagnetic wires is shown. This switching effect is based on a rapid propagation of large Barkhausen jumps. Suitable wires for this effect are the so-called "Wiegand wires", which are twisted and formed from a special ferromagnetic alloy. Special pulse wires can also promote this type of switching effect. Such a pulse wire comprises a compound element, which is formed as a wire-shaped core, and a surrounding casing. The core comprises a comparatively soft magnetic material (with a coercive field strength, H.sub.c1, between about 0.2 A/cm and 20 A/cm). In order for an external magnetic field (e.g., a switching field) to produce a rapid, abrupt change in flux in this core and a consequent reversal in the direction of magnetization, the core must show a pronounced uniaxial magnetic anisotropy with a preferential magnetic direction lying in its longitudinal or axial direction. Furthermore, to prevent the formation of unwanted terminating domains when the core has a relatively modest length, a comparatively harder magnetic material is selected for the casing (having a coercive field strength, H.sub.c2, of at least 30 A/cm), so as to permanently magnetize the core in this manner.
With this core structure, a switching arrangement can be assembled using an appropriate pulse wire as a part of a magnetic field sensor. The pulse wire is situated in a coil winding, which surrounds it as a further component of the magnetic field sensor. A voltage pulse is induced in the coil winding if a spontaneous magnetization reversal is produced in the core of the pulse wire by an external magnetic switching field when a specific field strength threshold is exceeded (see also E. Kneller: "Ferromagnetismus", Springer-Verlag [Ferromagnetism, Springer Publishing House] 1962, particularly pp. 401-408). This voltage pulse can then trigger a control or switching operation with evaluating electronics arranged downstream from the coil winding. These types of pulse wires, having diameters between 50 .mu.m to 300 .mu.m, can be used without additional auxiliary power as threshold triggers for a multitude of sensor tasks such as speed sensors, linear position encoders, or linear current-value limiting detectors, for measuring magnetic fields or as magnetic-field-sensitive keys.
In the Siemens prospectus entitled "SIPULS-Speed Sensors with Pulse Wires", a magnetic-field sensitive device, which has several of these magnetic-field sensors and exhibits the aforementioned characteristics, is shown. This device comprises pairs of setting and resetting magnets positioned on a master wheel coupled to a motor shaft. When the master wheel rotates, these magnets pass several stationary magnetic-field sensors. If a setting magnet approaches a magnetic-field sensor, then the switching field strength is exceeded in its corresponding pulse wire and a voltage pulse is generated in the coil winding, which is wound around the pulse wire. The pulse wire is subsequently brought into a magnetic neutral position again by the resetting field of a resetting magnet. Thus, a voltage pulse only occurs if a setting magnet approaches the pulse wire. In a known device, several such magnetic field sensors are available. Therefore, the direction of rotation can be determined from the sequence of the voltage pulses generated at the magnetic field sensors.
Manufacturing these pulse wires and the coil windings surrounding them entails considerable expenditure. Moreover, the magnetic properties, in particular the required anisotropic conditions, are difficult to reproduce and adjust with sufficient accuracy in the wires. This results in the generation of varying pulses within a magnetic-field-sensitive device by the magnetic-field sensors having the same design.
There is a need for a magnetic-field-sensitive device having sensors with similar characteristics. There is also a need for a magnet-field-sensitive device that is easily manufactured having a low expense.